Dell Dimension 4700 series System will not boot up to OS

i have a dell dimension 4700 3.0 ghz, 1GB ram i added another 1GB DDR2 4200 533Mhz to the existing (2)x 512 3200 pc2 then started to get memory has changed press “F1 to cont or F2 to go setup. I selected F1 & got blue screen when i restarted the pc, I got the blue error Screen and it continually fails to startup to OS.

can anyone help if possible